When you open an image (instead of saving or downloading to disk), your browser creates an association between the kind of image you've opened and the program you've chosen to open it with. Any time you download another image of that type, the program you chose previously will automatically try to open it.

To break the association:

Explorer

In Explorer, select Internet Options... from the Tools menu (Explorer 5 and higher) or the View menu (Explorer 4).

NOTE: To keep the problem from reocurring the next time you download something from Netscape, choose Save File and IGNORE all the verbiage about picking applications, expanding Netscape's capabilities, etc.